Effects of opioid peptides on immunoreactive corticotropin-releasing factor release from the rat hypothalamus in vitro

Abstract Effects of opioid peptides on immunoreactive corticotropin-releasing factor (I-CRF) release from the rat hypothalamus were examined using a rat hypothalamic perifusion system and a rat CRF RIA in vitro. β-Endorphin (0.3 – 30 nM), dynorphin (0.3 – 30 nM) and FK 33–824 (1 – 10 μM) suppressed basal I-CRF release in a dose-dependent fashion. At 2.2 nM concentrations of these peptides, mean percent inhibition was 56 % for β-endorphin; less than 5 % for α-endorphin; 44 % for dynorphin; 23 % for leucine-enkephalin; 6 % for methionine-enkephalin; less than 5 % for FK 33–824; and less than 5% for D-ala 2 , D-leu 5 -enkephalin. The inhibitory effects of β-endorphin and enkephalins were completely blocked by naloxone, but those of dynorphin were only partially blocked. These results suggest that opioid peptides act through opioid receptors and inhibit I-CRF release from the hypothalamus under our conditions. Therefore, endogenious opioid peptides may have a physiological role in the CRF-releasing mechanism of the hypothalamus.